In China there is a famous dish called Ma Po Doufu 麻婆豆腐 and most of the recipes I find online have pork. I was wondering if anyone knew if pork was an essential part of the dish (in terms of flavoring) or if there was something you could do to make it a vegetarian option? Would the dish work with chicken/beef?
A number of Chinese restaurants are happy to prepare it without pork or beef. I've seen it with pork (most common) or beef (sometimes).
A vegetarian Chinese place that I occasionally visit uses a "vegetarian ham" along with some vegetables like peas to augment the custardy texture of the soft tofu. I like to add some ja tsai (zasai, depending on romanization preferences) pickles in there, though I'd guess that's not that common.
Pork is not absolutely essential to the identity of the dish, but it's certainly the most likely version to be served.
The main replacement for the pork is mushrooms (he recommends a mix of wood ear, morel, and porcini), because of the good match in flavour. To get the texture he uses the Chinese technique of "dry frying", typically used for meat. I'll leave it to Mr. Lopez-Alt to explain the details - he does it better than I!
Using a combination of mushrooms as Kenji suggests (reconstituted shiitake plus plenty "normal" mushrooms), combined with finely crumbled (squeeze in your hand until you disintegrate the block, then drive the back of a fork through it) and well sauteed firm tofu (yes, adding tofu twice) yields an excellent texture here.
Dicing the mushrooms finely (brunoise-like size is best, but doing that to a pound of mushrooms is more work than you think :). DO NOT attempt to use a food processor, that tends to leave you with much mush and little room.) helps, as does sauteeing the tofu separately and adding some of your salt/sugar budget for the dish at that stage (it helps drive out the water).
Small TVP flakes also work reasonably well, as a substitute for the crumbled tofu or as an addition.
If one wants to avoid having soy tofu twice in the dish, burmese tofu (which you make from chickpeas) can be used as the topping too, but caution not to overcook it is advisable.
For some extra umami, adding some finely cut/broken douchi (salted black beans) in with the aromatics works great.
There a a lot of variants of Mapo Doufu.
I know of a vegetarian/vegan version that replaces the minced pork with fermented black beans (Douchi). Works very well. There is a recipe in the book Every Grain of Rice by Fuchsia Dunlop. An online version can be found here
Another version i know is with minced beef. I don't know the source.